The present invention relates to horizontal directional drilling, also known as trenchless drilling and, in particular to a drill bit component of an apparatus used for such drilling.
Horizontal directional drilling techniques have been used to drill boreholes generally horizontally beneath structures such as roadways or obstructions that are not to be disturbed. Such boreholes can be used to enable objects such as cables, pipelines etc. to be passed beneath the roadway without damaging the roadway or interrupting travel thereon.
Apparatus for performing such drilling is described for example in U.S. Pat. No. 4,953,638, and depicted herein schematically in FIG. 8. The apparatus includes a machine 10 disposed on one side of a structure, such as a roadway 12 beneath which a borehole 14 is to be drilled. The machine supports and rotates a rear end of an elongated drill string 16 which comprises a series of interconnected pipes and a drill bit 18 mounted at the front end of a forward-most pipe. The rear end of the drill string is rotated, causing the drill bit to cut through the soil. Simultaneously, the drill string is advanced in a generally horizontal direction. Periodically, the drilling is stopped to enable a new section of pipe to be attached to the rear of the drill string. Eventually, the drill bit 18 emerges through the soil at the other side of the roadway to completed the borehole. Then, a cable, pipeline, etc, can be inserted through the borehole.
The drill bit can assume different configurations, such disclosed in U.S. Pat. Nos. 5,647,448 and 6,247,544, for instance. In U.S. Pat. No. 5,647,448 a duckbill-shaped drill bit for trenchless drilling is disclosed which comprises a bit body having a plurality of teeth mounted therein. The teeth are in the form of carbide tips mounted in a front free end of the bit body. First and second sets of teeth are disposed on respective sides of a longitudinal center axis of rotation of the bit body. The teeth of the first set are oriented asymmetrically with respect to the teeth of the second set with reference to the axis, whereby the teeth of each set do not precisely track the teeth of the other set as they break through hard materials such as rock. Each tooth has a rear end that is mounted in a respective pocket (hole) drilled into the bit body.
The drill bit disclosed in U.S. Pat. No. 6,247,544 includes a bit body having a series of notches cut into a front end thereof. Cutting teeth are welded to respective notches. Each tooth comprises a carbide tip mounted on a steel tooth body (i.e., a composite arrangement), the steel body being required in order to be weldable to the steel bit body. A shortcoming of such an arrangement is that the teeth have backsides (considered with reference to the direction of rotation) which are unsupported by the bit body (unlike the teeth of U.S. Pat. No. 5,647,448 wherein the teeth are mounted in pockets (holes). Thus, not only are the composite teeth of U.S. Pat. No. 6,247,544 more expensive to manufacture (due to the need to bond a carbide tip to a separate steel tooth body), they can tend to break off if the shear forces overcome the weld forces.
Accordingly, it would be desirable to provide a novel drill bit for trenchless drilling which utilizes teeth that: do not have to be in the form of composites, do not require the drilling of holes into the bit body, and are supported at their backsides.
The present invention relates to a drill bit for trenchless drilling. The drill bit comprises a generally flat bit body which includes first and second side surfaces that are separated from one another by a thickness of the bit body. The bit body further includes a front cutting end and a rear mounting end adapted to be mounted to a rotary drill string. The bit body defines a longitudinal center axis extending through the mounting end and the cutting end. The cutting end includes a front edge, and first and second grooves formed in the first and second side surfaces, respectively. Each groove defines a generally forwardly facing shoulder spaced rearwardly from the front edge and being exposed to the front edge by a plurality of slots formed in the respective first and second side surfaces. Each slot extends from the front edge to a respective groove in a direction oriented generally radially with reference to the front edge. The slots associated with each groove are spaced apart from one another along the front edge by lands formed by the bit body. Each land includes a rear end spaced forwardly from and facing the respective shoulder. The grooves and the slots extend only partially through the thickness of the bit body from the respective first and second side surfaces, wherein the bit body defines a floor extending from each shoulder to the front edge. First and second sets of cutting teeth are mounted to respective ones of the first and second side surfaces and are disposed on opposite sides of the axis. Each tooth includes a front cutting end, a rear mounting portion mounted in a respective one of the slots. Each mounting portion rests upon the floor associated with the respective slot, and a rear end of each tooth abuts against a respective one of the shoulders. The first set of teeth is arranged asymmetrically relative to the second set of teeth with reference to the axis.
Preferably, the front edge is convexly curved, and the shoulder is convexly curved correspondingly to the curvature of the front edge.
The present invention also relates to a method of manufacturing a drill bit for trenchless drilling. The method comprises the steps of:
(A) providing a bit body having first and second side surfaces, a rear mounting end, and a front cutting end, and defining a longitudinal center axis extending from the mounting end to the cutting end;
(B) milling a groove into the first side surface of the bit body, wherein the groove is spaced rearwardly from a front edge from the bit body and forms a forwardly facing shoulder;
(C) milling a plurality of slots in the first side surface, wherein each slot extends from the front edge to the groove in a direction generally radially with reference to the front edge, the slots are spaced apart along the front edge, wherein the bit body forms lands disposed between adjacent slots, each land including a rear end spaced forwardly from and facing the shoulder, the slots and the groove forming a floor extending from the front edge to the shoulder;
(D) positioning cutting teeth in respective ones of the slots such that each tooth includes a front cutting portion, and a rear end abutting the shoulder;
(E) securing the teeth to the bit body; and
(F) performing steps A-D with respect to the second side surface, wherein the teeth associated with the first side surface define a first set of teeth disposed on a first side of the axis, and the teeth associated with the second side surface define a second set of teeth disposed on a second side of the axis, the first set of teeth arranged asymmetrically relative to the second set of teeth with reference to the axis.